This invention relates to a method of, and a stylet apparatus for, installing a retrograde coronary cannula.
Cardioplegia is a commonly used technique for protecting the heart during heart surgery in which a cooled cardioplegia solution, for example a potassium solution, is circulated through the heart. The cardioplegia solution stops the heart and reduces its temperature to minimize damage to the heart. Cardioplegia is often administered through the aorta in the antegrade direction, i.e., the direction of normal blood flow. However, there is increasing interest in administering cardioplegia in the retrograde direction, i.e., opposite the direction of normal blood flow. Retrograde administration of cardioplegia has been used in patients having critical coronary artery stenosis that would have made the antegrade administration of cardioplegia difficult and inefficient, and with patients suffering from aortal valve disease. A retrograde sinus catheter particularly adapted for the retrograde administration of cardioplegia is disclosed in U.S. patent application Ser. No. 07/874,589, filed Apr. 27, 1992, incorporated herein by reference.
There are two principle techniques for installing a coronary cannula in the coronary sinus for the administration of cardioplegia. The first is known as the "open atrium" technique in which the right atrium of the heart is substantially opened with a large incision so that direct access is provided to the coronary sinus. A disadvantage of this technique is that it makes it more difficult to drain venous blood from the vena cava and to drain blood from the right atrium. An alternative is to use a "blind" procedure in which only a small incision is made to gain access to the right atrium and the coronary sinus. It can be very difficult to manipulate the coronary cannula, which is typically small and flexible, into the proper position in the coronary sinus through this small puncture.
Generally, the method of installing a coronary cannula according to this invention comprises providing a coronary cannula with a stylet extending through the lumen of the cannula. The stylet has a handle and a shaft that extends through the lumen with a stiff but flexible proximal portion, and a deformable distal portion. The shaft is sufficiently long that the deformable distal portion extends generally to the tip of the coronary cannula. The tip of the coronary cannula is then shaped by deforming the deformable distal portion of the stylet inside the lumen to facilitate its insertion through an incision in the right atrium and into the coronary sinus. The tip of the coronary cannula is then manipulated into the coronary sinus by steering the shaped tip by manipulating the handle. After the tip of the coronary cannula is in place, the cannula is anchored, for example by inflating a balloon at the tip of the cannula provided for that purpose, and the stylet can be drawn from the lumen of the coronary cannula.
Generally, the stylet apparatus for installing a coronary cannula according to this invention is adapted to fit inside the lumen of a coronary cannula to facilitate the installation of the cannula into the coronary sinus. The stylet comprises a handle, and a shaft extending from the handle and adapted to fit inside the lumen of the cannula. The shaft comprises a stiff but resilient proximal portion and a deformable distal portion that can be permanently deformed to a desired shape when inside the cannula to hold the tip of the cannula in a preselected shape to facilitate the insertion of the cannula into the coronary sinus. In the preferred embodiment the shaft comprises a malleable steel wire and a tube surrounding the proximal portion of the wire, stiffening the proximal portion of the shaft while leaving the distal portion of the wire uncovered. The deformable distal portion of the stylet is shorter than the stiffer proximal portion so that the deformability of the distal portion does not interfere with the steering of the tip, as described below. The distal portion of the stylet may be colored so that the surgeon can gauge the depth of penetration of the stylet and cannula in order to facilitate proper placement of the cannula.
The coronary cannula is preferably provided with the stylet already in the lumen, although they could be provided separately, and the stylet inserted into the lumen before the installation of the cannula. With the stylet inside the lumen of the coronary cannula, the tip of the coronary cannula can be configured to pass readily through an incision in the right atrium and into the coronary sinus. The malleable distal portion of the stylet holds the tip of the cannula in the desired preformed configuration, while the stiffer, flexible proximal portion of the stylet allows the cannula to flex and bend sufficiently as the tip of the cannula is manipulated into the coronary sinus.
The method of installing the coronary cannula and the stylet apparatus for installing the cannula allow the cannula to be quickly inserted into the coronary sinus for the prompt administration of cardioplegia solution. The stylet apparatus also helps the surgeon gauge the depth of the tip to facilitate proper placement. The method and apparatus provide for the accurate placement of the cannula, and hold the cannula in place until it is anchored, for example by inflating a balloon on the cannula.
These and other features and advantages will be in part apparent, and in part pointed out, hereinafter.